I think Blink's LayoutNG project and Servo both show that you can rewrite your layout implementation (and Servo also having a new style implementation, now in Firefox as Stylo). I think both of those serve as an existence proof that it's doable.

It's doable if you already have a large team of experienced web engine development experts, a multi-million budget and years to spend on just planning.

Implementing an open standard shouldn't be like this. Even proprietary formats like PDF are much simpler to implement than CSS.

TCP/IP is an open standard, yet I suspect you would have the same problems implementing it (Microsoft famously copied BSD stack at first).

You could probably say the same thing about any complex open standard, like FTP etc.

A minimal, 80% PDF, maybe. A complete PDF? No.

It's not doable, part from when it is.

'Open standard' has nothing about something being simple and straight forward. What CSS is trying to do is complicated because of a whole bunch of pragmatic reasons.

Last time a browser tried to 'move things forward', ngate aptly summed it up as

    Google breaks shit instead of doing anything right, as usual.
    Hackernews is instantly pissed off that it is even possible to
    question their heroes, and calls for the public execution of
    anyone who second-guesses the Chrome team

I never claimed that the existing browser vendors can’t do it incrementally — they certainly can. What I wrote was: “... there's not going to be another web browser engine created by an independent party.”

Isn't Grid and Flexbox supposed to be that sane layout system? At least that's what I've heard from those who have used them.

Even if Grid and Flexbox are awesome and perfect and the solution to all our problems, they don't make everything else in css suddenly disappear, a new layout/render engine still has to implement every bit of it, quirks included.

React Native has what seems like a pretty sane css-like layout system. Maybe this could become the basis for a "css-light" standard that could gradually replace the existing css, and offer much faster performance for website authors who opt in.

I presume parent's point is about how they then interact with other layout modes (what if you absolutely position a flex item, for example), along with the complexity of things that rely on fragmentation (like multicol).